Stopwatch

How this stopwatch stays accurate

Most naive stopwatches add a fixed amount every interval - say 10 milliseconds each tick. The trouble is that browser timers are not guaranteed to fire on time, and they are deliberately throttled to roughly once per second when a tab is in the background. Count ticks and your timer drifts, losing seconds or even minutes over a long session.

This one records the real timestamp when you press start and, on every screen refresh, subtracts it from the current clock. The display is just a view of "now minus start", so it is correct to the millisecond no matter how irregular the refreshes were. Leave it running in another tab for an hour and it will show the right time the instant you come back.

Lap times and totals

Press Lap (or the L key) to freeze a marker without stopping the clock. The table records two numbers for each lap: the lap time, which is the gap since the previous lap, and the total, which is the full elapsed time at that moment. Timing intervals on a run, rounds of a workout or stages of a task all become easy to compare afterwards.

Handy for

• Interval training, where each lap is one round
• Cooking or brewing steps you want to log without resetting
• Timing how long tasks actually take, to plan better next time
• Speed-solving, sport drills and classroom activities

Need to count down instead of up? Use the countdown timer with its alarm, or the Pomodoro timer for focused work sessions. To add up several recorded durations, the time calculator does the arithmetic for you.

Frequently asked questions